Various objects are moved in an automated fashion. To ensure controlled movement of the object the relative position of the object must usually be known (at least during certain portions of the object's travel and trajectory). For example, when the object comprises a movable barrier that moves pursuant to the motive facilitation of a corresponding movable barrier operator, relative position of the movable barrier with respect to known obstacles (such as a floor, wall, or other fixed barrier) should be known in order to aid in ensuring that the automated mechanism does not mis-position the movable barrier with respect to such an obstacle and thereby potentially damage the movable barrier, the obstacle, and/or the movable barrier operator mechanism or other persons or property in the vicinity of the impact.
Various solutions are known in the art to facilitate knowing the present likely position of a moving object. One simple solution makes use of so-called limit switches. These are mechanically actuated switches that are usually placed in a fixed location of interest (such as near a desired end-of-travel location for the movable barrier). Such switches are closed when physically contacted by the movable barrier and can serve to signal a controller that the movable barrier has at least reached a position that corresponds to the location of the limit switch.
While suitable for many settings, there are some scenarios when such switches provide less than satisfactory service. This method of knowing the position does not readily facilitate automatic setup of the travel for the moving object. This, in turn, allows limits of travel to be set correctly or incorrectly as ordained by an installer. For example, when an installer sets the limits of travel he or she can set the stop position a long distance from the true end of travel.
Another prior art approach provides for the generation of signals that each correspond to a particular amount of travel for the object in question. For example, many movable barrier operators use magnetic or light sensitive sensors to detect rotation of a motor (or other motive linkage) that drives movement of a corresponding movable barrier. These pulses are then counted during a learning mode of operation to ascertain the number of pulses that are required to move the object from a first position to a second position. That count is then used during normal operation to measure and detect a present position of the moving object.
Again, unfortunately, such an approach, while providing satisfactory service in some circumstances, often leaves much to be desired. For example, when used with a movable barrier operator, such an approach is highly subject to slight shifts in the physical position compared to the count (due to missed or additional counts, or power loss while in travel). Such slight shifts can give rise to small errors that, over time, can accrue to a significant extent. Such an accrued error will, in turn, cause the movable barrier operator to mis-locate a present position of the movable barrier and again potentially permit or even cause an inappropriate attempted positioning of the movable barrier with respect to an obstacle such as a floor, wall, gate frame, or the like.
Passpoint-based schemes have been proposed to supplement such count-based approaches. Such systems typically provide for the generation of a passpoint event during ordinary travel of a corresponding object, such as a movable barrier, between two or more expected positions. This passpoint event can comprise, for example, a discrete light signal that is independent of the signals that are used to generate the above-described count and will usually be generated through an independent passpoint event generator that responds independently to some indicia of object movement. In theory, such a passpoint event can be utilized as a known fixed location as corresponds to movement of the moving object. Accordingly, the count can then be maintained as a function of that known fixed location to avoid the accrued error circumstances that can otherwise afflict such count-based systems.
Unfortunately, during initial installation the passpoint event has to be placed in the travel somewhere between the limits. This usually entails the passpoint being set to a specific position and the installer being required to install the unit in a specific location. If the installer does not accurately follow the installation procedure, the passpoint can be placed in a location that is not between the limits of travel. Under such circumstances, the movable barrier then has no passpoint event against which to calibrate its count or other position-determining processes.
To attempt to resolve such problems as these, other prior art suggestions provide for a plurality of passpoint events instead of only a single such event during any reasonable extent of movable barrier travel. So configured, at least one passpoint event will likely be detected during a learning sequence and thereby provide a basis for comparison to determine the accuracy of a present count and/or to re-calibrate the perceived position of the movable barrier with respect to the passpoint event. Again, however, such a solution has only begot yet other problems. In particular, it is possible for a movable barrier operator to become uncalibrated with respect to which passpoint event, of many detectable passpoint events, comprises the particular passpoint event against which location of the movable barrier can be firmly ascertained and measured.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.